I purchased PS to address my issue with 85000 images of which many are duplicates from several replacement laptops, etc, etc. I was advised pre purchase that LR or PS would identify any duplicates at the point of import but it didn't and I still remain perplexed if is possible without having to export all the images and purchase a 3rd party product that would deal with the duplicates then reimport. I hope this isn't the case because advisors at Abode advised me that PS/LR would do this and thats the primary reason I purchased it. They won't cancel the membership and now I left with a forum. please help
Not possible in Photoshop .
Moreover this is a Lightroom Question.
I will give you an idea how to do that.
Import images to Lightroom from folder A
Now try to import images from folder B, if folder B have the same images that are already in Lightroom , it will show those images as grayed out.